Japanese Laid-Open Patent Application No. 58-20538 discloses a technique in which a user may select an operation from among various operations using a single key depending on the pressing (operating) time period of pressing the single key.
Japanese Laid-Open Patent Application No. 08-329315 discloses a guidance control method including, when a user presses a key on a guidance screen, measuring a time period of pressing the key, determining a type of reaction sound, a method of switching the guidance screen, and contents and speed of audio guidance and the like based on the measured time period.